Such drive units can be used, for example, for driving windshield wipers, electric windows, mirrors, seats, as well as entire doors. With special preference, such drive units can be used for realizing a central locking function in motor vehicle door locks. Advantageously, such drive units are also used in conjunction with so-called electric locks, i.e. such motor vehicle door locks where an obligatory locking system is opened by means of a motor.
For this purpose, drive units of this type are often equipped with a gear, specifically a worm gear, on the output side. In this case, on the output side on the motor shaft, a worm shaft is arranged that meshes with the outer teeth of a worm gear. Rotary movements of the worm gear in different directions have the effect of subjecting the motor shaft to an alternating axial load during its operation. Due to these different axial loads, in the prior art knocking noises are generated when the motor shaft exhibits longitudinal play between a motor-side and a gear-side axial stop.
In order to control this longitudinal or axial play of the motor shaft, different solutions are pursued in the prior art. EP 0 764 099 B1, which characterizes the type, discloses a drive unit with an electric drive motor followed by a worm gear. In addition, pre-tensioning spring elements are provided that push elastically against the free face surface of the worm shaft. These spring elements consist of a leaf-spring-type spring element that is aligned transversely to the axis of rotation of the worm shaft and is fixed with its opposite end edges on shoulders of the associated housing. Between the end edges, there is a central section that contacts under pre-tension the face surface of the worm shaft.
Comparable drive units are disclosed in U.S. Pat. No. 5,169,245 and EP 0 133 527 B2. In the former case, a motor shaft is provided in a drive unit that is supported on a spring element via a ball. The variant according to EP 0 394 512 A1 works with an axial disk that is arranged axially in face of a shaft end of the motor.
Such designs in the prior art are structurally relatively complex and need to be manufactured in several stages. According to U.S. Pat. No. 3,169,245, not only is an end-side steel ball provided, but there is also a plate contacting the ball that is supported in a mount by means of a spiral spring. EP 0 394 512 A1 operates with a specially shaped start-up disk that is additionally equipped with an upstream set screw that is supported on the housing. The final citation, EP 0 764 099 B1, employs a spring element that, in a top view, is essentially shaped like a rectangle whose end edges on the shorter sides of the rectangle are bent at an angle of at least 30° towards the same side out of the plane of a central section. This, too, is costly in terms of manufacture and assembly.